Note: The accumulator only maintains sufficient pressure for lowering the grapple for approximately 1.5 minutes after the engine stops. The grapple cannot be lowered by this method after this time limit.
When you test or you charge the pilot oil accumulator, the pressure in the pilot hydraulic system must be released. The temperature of the nitrogen gas must also be taken into account. The pressure and volume of dry nitrogen gas varies with temperature.
Test
- Ensure that the oil in the hydraulic system is at normal operating temperature. Park the machine on a smooth, level surface.
- Engage the parking brake.
- Install the steering frame lock. Block the wheels. Raise the arch and the grapple.
- Stop the engine.
- Press the grapple control lever forward in order to lower the grapple. You should be able to lower the grapple up to 1.5 minutes after the engine has stopped.
 | |
| Illustration 1 | g01210648 |
Grapple Control Lever | |
- Lower the grapple to the ground. If the grapple will not lower, perform the procedures in the "Charging" section.
Charging
Note: The 170-8531 Pilot Oil Accumulator that is installed on the machine from the factory is not serviceable. If this accumulator needs service, replace this accumulator with the 179-9387 Pilot Oil Accumulator that is rechargeable. The following procedure can be performed on the serviceable accumulator.
| Required Tools | ||
| Part Number | Description | Quantity |
| 152-2023 | Nitrogen Charging Group | 1 |
The pressures in the following table are for an ambient air temperature of 21°C (70°F). Adjust the pressure for other ambient conditions, as required.
| Accumulator Precharge Pressure/Temperature Relationship for the 690 kPa (100 psi) Pilot Oil Accumulator |
|
| Temperature | Pressure |
−7°C (20°F) |
625 kPa (91 psi) |
−1°C (30°F) |
638 kPa (92 psi) |
4°C (40°F) |
651 kPa (94 psi) |
10°C (50°F) |
664 kPa (96 psi) |
16°C (60°F) |
677 kPa (98 psi) |
21°C (70°F) |
690 kPa (100 psi) |
27°C (80°F) |
703 kPa (102 psi) |
32°C (90°F) |
716 kPa (104 psi) |
38°C (100°F) |
729 kPa (106 psi) |
43°C (110°F) |
742 kPa (108 psi) |
49°C (120°F) |
755 kPa (110 psi) |
 |
Dry nitrogen is the only gas approved for use in the accumulators. The charging of oxygen gas in an accumulator will cause an explosion. An explosion can be eliminated by using nitrogen gas cylinders with standard CGA (Compressed Gas Association, Inc.) No. 580 connectors. When nitrogen gas is ordered, make sure to order the cylinders with CGA No. 580 connectors. Do not rely on color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders. In any application, never use an adapter to connect your nitrogen charging group to a valve outlet used on both nitrogen, oxygen, or other gas cylinders. BE SURE YOU USE DRY NITROGEN (99.8% purity). |
 |
| NOTICE |
|---|
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates. |
Nitrogen gas pressure varies with the temperature. To obtain the most accurate nitrogen charge, the temperature of each accumulator must be identical to the air temperature around the accumulator.
If an accumulator has less than half of the required amount of precharge pressure, the accumulator should be charged. Then charge the accumulator again after you use the grapple control lever repeatedly in order to prevent trapping oil in the accumulator. Oil in the accumulator will give an inaccurate precharge reading.
However, the temperature of the accumulator could be higher than the air temperature around the accumulators. In this case, the temperature of the accumulator should be used instead of the surrounding air temperature.
 | |
| Illustration 2 | g00904132 |
The pilot accumulator is located inside the compartment on the right side of the cab.
- Ensure that the oil in the hydraulic system is at normal operating temperature.
- Stop the engine. Move the grapple control lever repeatedly until there is no pilot pressure.
- Remove cap (1) and O-ring seal (2) from the accumulator.
 | |
| Illustration 3 | g00535595 |
Accumulator (1) Cap. (2) O-ring seal. (3) Screw. (4) Accumulator valve. | |
- Loosen screw (3) with half of a turn. Use an allen wrench to loosen screw (3) .
- Use the pressure gauge in the 152-2023 Nitrogen Charging Group to check the nitrogen charge in the accumulator.
 | |
| Illustration 4 | g00535589 |
Nitrogen Charging Group (5) Charging hose fitting. (6) Pressure gauge. (7) Valve body. (8) Knob. (9) Accumulator purge valve. (10) Charging hose. (11) Adapter. | |
- Screw adapter (11) onto accumulator valve (4) .
- Open accumulator valve (4) with knob (8). When the needle of the pressure gauge begins to move, turn knob (8) with one complete turn. Check the temperature of the air around the accumulator. The reading on the pressure gauge must be within the tolerances in Table 2.
The pressure gauge is now showing the precharge pressure of the accumulator.
- If the reading on the pressure gauge is too high, slowly open accumulator purge valve (9) in order to lower the pressure. If the reading on the pressure gauge is too low, use the following procedure to charge the accumulator:
- Connect charging hose fitting (5) and charging hose (10) to the nitrogen cylinder.
- Close accumulator purge valve (9) and open the valve on the nitrogen cylinder. Refer to Table 2 for the correct charging pressure.
- Slowly open accumulator purge valve (9) and charge the accumulator. Then, close accumulator purge valve (9) .
If the pressure reading on the pressure gauge decreases, open accumulator purge valve (9) and allow more nitrogen to fill the accumulator.
Make sure that the reading does not change when accumulator purge valve (9) is closed.
- Close accumulator purge valve (9). Close the valve on the nitrogen cylinder.
- Close accumulator valve (4) with knob (8). Remove the test equipment.
- Use an allen wrench to tighten screw (3) .
Torque for screw (3) ... 20 N·m (15 lb ft)
- Check for leaks by spraying soapy water onto accumulator valve (4) .
- If there are no leaks, install cap (1) and O-ring seal (2) onto the accumulator.
- Proceed to the "Test" section.